Refractometer employing photosensitive devices and use of the same



Sept. 27, 1949.

R. M. PIERSON REFRACTOHETER EMPLOYING PHOTOSENSITIVE DEVICES AND USE OFTHE SAME Filed May 2, 1945 INVENTOR ROBERT M. /ERsoN ATTORNEY PatentedSept. 27, 1949 UNITED STATES PATENT OFFICE REFRACTOMETER EBIPLOYLNGPHOTOSEN- SITIV E DEVICES AND USE OF THE SAME Robert M. Pierson, Hudson,Ohio Application May 2, 1945, Serial No. 591,468

(Cl. 3l6-32) 18 Claims. 1

This invention relates to reiractometers enrpioying photosensitivedevices and to their use in measuring and controlling the composition ofa fluid, etc. More particularly, the invention relates to following a.refracted beam or beams, the follower or followers being used forindicating or recording changes in the fluid, etc. The inventionincludes both the process'end apparatus therefor.

In the chemical industries where knowledge of the composition of anyfluidv being treated is desired, this can, in many instances, bedetermined through changes in the angle of refraction of a beam ofradiant energy passed through it. The fluid must be translucent to theradiant energy, and other conditions must be kept constant, orcorrections must be applied. For instance, in the case of a liquid, itstemperature as well as its composition will affect the refractive index;and in the case of a gas the refractive index is dependent on both itstemperature and pressure as well as its composition.

According to one embodiment of this inven tion, by following cl'iangesin the angle of refraction of a beam of radiant energy of a particularwave length passed through a fluid, its composition may be indicated orrecorded. Also, such changes may be utilized to bring about some desiredresult. For instance, in concern-- trating a solution, when the angle ofrefraction reaches a predeterminedvelue, further concentration may beprevented, or some ingredient may be added, or the cooling of thesolution may be initiated, or the solution may be transferred to anothervessel, etc. In the handling 01' a dangerous gas, a change in therefractive index may be followed; and when a. predetermined maximum isreached, an alarm may be given to indicate that an explosive or toxiccomposition has been formed. Gases under pressure lend themselves to thepurposes of this invention better than gases at atmospheric pressure.

According to a further embodiment of my invcntion, changes in thedifference in refractive indices of a fluid at two or more segregatedwave lengths i. e, changes in the refractive dis-- persion of afiuid-a-re used to determine or com trol, etc., the composition of thefluid. in ham dling or treating mixtures of components havingsubstantially the same refractive index at a particular wave length, itwill often be found advantageous to use changes in the refractivedispersion instead of changes in the refraction of a single beam. Asexplained below, one important advantage in this lies in the fact that,

in general, the dispersion of a substance is considerably less affectedby temperature changes thanis its refractive index.

It is an advantage of this invention that the recording, etc., iseffected without bringing a sensitive element into physical contact withthe fluid and without the attention of some one being devoted to makinganalyses, etc. Furthermore, the human element is minimized or totallyeliminated. The only limit to the applicability of the invention is therequirement that the fluid being measured be sufficiently translucent toradiant energy of some particular Wave length or wave lengths to whichphotosensitive apparatus is responsive.

It is an important advantage of the invention that the eflicientoperation of the method and apparatus is not vitiuted by changes inthose optical properties of the fluid, such as absorption and turbidity,which might be very large relative to the changes in refractive indexand con"- position.

r pingence or According to my invention the fluid being measured iscontained in or run continuously through a hollow container and refractsone or more beams of collimated. monochromatic radi ant energy, thedirection of whose emergent path serves to measure or control thecomposition of the fluid or effect some other operation by theimpingence of the beam or beams on photosensitive apparatus; Althoughnot necessary, it will often be convenient to use a beam or beams whosecross section is exceedingly small, the operation being reflected by theimnonimpingence of substantially the cntire'transverse area oi therefracted. beam on a light-semitivc surface or segregated portionsthereof.

The operation does not rely on the relative proportion or the beamintercepted by a lightsensitive surface. It does not depend uponmeasuring the varying amounts of current generated in the photosensitivedevice correspond ing to the interception of varying proportions of thebeam. of radiant energy but requires only that at times some detectableamount of current be generated by impingence of any portion of. theradiant energy of a beam on the photosensitive area and that at othertimes no current at all be generated due. to nonimpingency of the beamon any portion thereof. The shape of the beam is immaterial. At times itmay be desirable to use a. beam of small cross-sectional area, such asshown in the drawings, but this is not necessary because the narrow edgeportion of a.

wider beam may, likewise, be employed. Thus, the location of the edgesof the beam first intercepted by the photosensitive surfaces will be ofimportance (the beam being nondivergent due to the monochromaticity andthe collimation of the radiant energy), and shifts in the direttion ofthe beam whose dimension in the line of travel will bring varyingproportions of the beam on the photosensitive surfaces are, therefore,not intended to affect the operation of the device.

The invention will be further described in connection with theaccompanying drawings in which:

Fig. 1a is an elevation, largely diagrammatic, of apparatus forgenerating a coilimated beam of radiant energy and passing it through afluid with means for recording changes in its angle of refraction;

Fig, 1b is a plan view of the same showing more completely the equipmentfor adjusting the position of the photocells;

Fig. 2 is a plan view of a portion of the apparatus shown in Fig. 1b,with the photocell carrier equipped with maximum and minimum stops;

Fig. 3 is a plan view of photocells equipped with direct control means,though not equipped for indicating or recording; and

Fig. 4 is a plan view of means adapted to utilize changes in therefractive dispersion of beams of different wave length.

In Figs. la and 1b the fluid l flows through the hollow prism 2 (shownin section in Fig. 1b) which has faces 3 and I transparent to theradiant energy. A mercury lamp 5 is used as the source of monochromaticlight whose radiant energy is diffused by the screen 6, collimated bythe lens 1. For the purposes of illustration, a narrow beam 8 is shownwhich passes through the slits 9 and Ill and whose undesirable wavelengths are eliminated by filters l Two photocells l2 and [3 are mountedon the movable carriage H! which slides upon the fixed ways l5. They aredisposed adjacent to the closely spaced mirrors I6 and i! so that lightintercepted by either mirror will be reflected into its adjoiningphotocell. The carriage I4 is connected to a pen arm 18, pivoted toswing about the fixed point l9 and which records on the chart 20. Theposition of the carriage I4 is regulated by the reversible motor 2|which is operated by an external source of current (not shown) througheither of the photocells l2 or l3 and suitable amplifying apparatus 22.

In operation, the refracted beam 8 will have an emergent directiondependent only upon the refractive index of the fluid and will impingeupon a null point 24 between the mirrors l6 and H. An increase in therefractive index of the fluid causes the beam to move so as to impingeupon the mirror l6 and thus on the photocell l2. The electrical impulsethus generated and amplified causes the motor 21 to turn in a directionsuch that the carriage M, to which it is connected by the geararrangement 25, will move to a point where the beam is again in the nullposition between the mirrors l6 and IT. This moves the pen arm l8 whichrecords the change on the chart 20. Conversely, a decrease in therefractive index of the fluid will cause the beam to impinge upon themirror I! and thus the photocell l3, resulting in the motor's turning inthe opposite direction.

The width of the null point between the mirrors is approximately that ofthe slits 8 and I0 and,

therefore, also equal to that of the beam at its point of impingencesince the beam is not diverged or dispersed due to its collimation andmonochromaticity.

It is evident that the sensitivity of the instrument can be enhanced toany desired degree by mere prolongation of the optical path bet een theprism and the photocell, such increases .a sensitivity being, ingeneral, limited only by the accuracy with which it is possible tomeasure and compensate for other properties of the fluid affecting itsrefractive index, such as temperature. By adjustment of the amplifyingappsratus so that only a minute amount of incident radiant energy isrequired to actuate the motor, the system is made independent of therelative energy content of the beam, providing Olly that it is abovesome lower limit. The operation of the instrument is, therefore,independent of large variations in other optical properties of thefluid, such as absorption and turbidity, which may occur concurrentlywith negligibly small changes in its refractive index but which wouldsubstantially alter the energy content of the emergent beam. Similarly,fluctuations of the intensity of the radiant energy source, such asmight be caused by line voltage surges, or gradual change in theemission characteristics of the source with time will have no effect onthe accurate operation of the instrument. Also, the operation isunaffected by changes in the photocell emission characteristics.

Instead of passing the beam through a segregated flowing fluid, it maybe passed through a stationary or agitated fluid in a reaction vessel orthe like.

Although not ordinarily the most desirable method, the source of theenergy might be located within the fluid so that it passes directly intothe fluid without first passing through the surr0unding atmosphere.Likewise, the beam may be made to impinge upon a reflecting surfacewithin the liquid whose plane is at an angle to the plane of thetransparent face through which the beam passes, so that changes in thedirection of the reflected beam are utilized. In these alternativearrangements for obtaining the same end as hav ing the fluid flowthrough a prism, the operation of the instrument by effecting control byimpingence or nonimpingence of the entire beam or any substantialportion of it on the light-sensitive surface remains the same.

In Fig. 2 the carriage 26, whose position is adjusted as the directionof the beam changes, is connected with an operating arm 21. When thedirection of the beam reaches a predetermined maximum or minimum, aconducting point on the arm 21 makes contact with the point 28 Or 29,thereby closing one circuit or the other and setting in motion thereby amotor or valve or other mechanism to effect some desired result. Suchequipment might, for example, be used in a mine where the maximum andminimum refractive indices might be used to set off different signals todenote that the composition of the gas had become explosive or theoxygen content had become dangerously low, etc. The pen arm 30 is forrecording as in Figs. la and 1b.

In the arrangement shown in Fig. 3 the energy output of the separatephotocells 35 and 36 produced by changes in the direction of the beam 31operates auxiliary amplifying apparatus 38 which, in turn, through theconnections 39 operates suitable valves, pumps or motors to control thefluid composition as its refractive index. increases or decreases, as byeither adding water or other diluent or adding a concentrate, etc. Thewidth of the null point 40 is variable and is preferably wider than thebeam by the amount of lateral travel between the mirrors 4! and 42,which the beam will make as it fluctuates within the allowable limits ofconcentration of the fluid.

In addition to measurement or control, etc., of a composition throughchanges in the refractive index at one wave length, changes in thedispersion of the fluid may be utilized. For this purpose changes in asecond beam of different wave length must also be considered. The secondwave length is preferably well segregated in the radiant energy spectrumfrom the first in order to obtain the advantages of the largest possiblechanges in dispersion. The fluid is contained in or run continuouslythrough a hollow container and refracts the beam of collimated radiantenergy whose spectral composition has been reduced to two monochromaticwave lengths by appropriate filters. The direction of the emergent pathof an element of the beam at one wave length serves to partially measureor control, etc., the composition of the fluid, as described inconnection with the preceding drawings. Using this beam element and itsassociated photosensitive devices as a reference, angular separationbetween it and the beam element of the second wave length, which isassociated with other photosensitive devices, serves as a measure of thedispersion and, therefore, of the composition of the fluid through whichthe beam haspassed.

By the use of a multiplicity of very closely spaced photosensitivesurfaces disposed in the range of the beam element of the second wavelength, a wide range of control or the initiation of numerous operationsis possible. The photocelis disposed adjacent the first beam element aremounted and equipped with means which causes them to follow this beamelement. The photocells disposed adjacent the second beam element areeither provided with means which causes them to independently followtheir beam or to move with the first-mentioned photocells. If thelatter, their movement may exactly duplicate that of the first-mentionedphotocells or the two sets of cells may move different dis tances, as bycausing one set of photocells to move but a fraction or multiple of thedistance of the other set.

If photocells are mounted on opposite sides of each beam element and areprovided with means which cause them to separately follow the respectivebeam elements as described in connection with the use of a single beamelement, the angular distance between the pairs of photocelis may bemeasured by mechanical linkages according to means well known in theart. Changes in the angle may be utilized in any desired manner.

Fig. 4 relates to equipment designed to take advantage of the changes inthe dispersion of refracted light from two beam elements of segregatedwave lengths. The light source, collimator, slits, filters. etc.,required to produce a coilimated beam of two monochromatic wavelengthelements are not shown as the equipment used may be the same as in Figs.la and lb, except that the filters are so chosen as to allow the passageof a second wave length. The beam 45 on passing through the hollow prism46 containing the fluid to be tested is refracted into the two elementsH and 48, the latter being of the carriage is equipped to follow thebeam 41 and keep it centered in the null point between the mirrors. Thepen arm 54 may be used to record the position of the carriage. or it maybe omitted.

Associated with the beam of shorter wave length 48 are the photocellsB5, 56, and 51 also ailixed to the carriage 53 but divorced from thecircuits which control its position. Thus,.as the composition of thefluid in the prism 4 6 varies so as not only to cause changes in thereference beam element 41 but also to cause changes in the angle betweenthe beam elements ll and 48. the beam element 48 will traverse the smallarc mirror 58 and be reflected separately into the photocells 55, 56,and 5'! or directed back upon itself. As the reflected beam elementinitiates responses in the several photocelis, a number of operationsmay be initiated corresponding to changes in the angle between thebeams, such operations being made optionally dependent upon orindependent oi the position of the reference beam element 41 and henceof the carriage 53.

Where advantageous, the arc mirror-58 and three photocells 55, 56, and51 may be replaced by two photocells and angled mirrors, such as shownfor use in connection with beam element 41, and these may be mounted ona carriage which operates independently of carriage 53, and

this carriage may be made to follow the beam 48 in the manner described.The movement of this other carriage may be used for recording or forcarrying out desired operations, for example, such as those suggestedabove.

It is to he understood that although mirrors are used in Figs. 1-4 fordiverting the beams on the photosensitive surfaces of the photocells,the beams may be made to fall directly upon these photosensitivesurfaces or on the surfaces of a multiple cathode photocell althoughordinarily the use of mirrors, as shown, will constitute a preferredarrangement.

The following examples. illustrate how the selleral types of equipmentshown in the drawings may be utilized. It is to be understood that theexamples are illustrative only, and the invention is not limited theretobut is of eneral application.

In the first example, assume that it be desired to measure or controlthe concentration of a sugar solution of approximately per centconcentration to the nearest 1 per cent. At 68" F. the refractive indexn of a 50 per cent sugar solution is 1.4200 for sodium 1) light, and

(In a -"0.0021

where c is concentration in per cent by weight of sugar. Referring toFig. 1 and. assuming the width of the beam 8 to be equal to the distancebetween the mirrors I5 and I! and that a change in concentration of 1per cent in the solution is to correspond to a lateral movement of thelight beam in the plane of the photocells equal to the 7 width of thebeam, and assuming for convenience that this width ofthebeam and thedistance between the mirrors are equal to 0.10 inch (the othercross-sectional dimension of the beam being preferably approximately thelength of the photocell cathodes), the placement of the elements of theapparatus shown in Fig. 1 may be as follows:

If the ways IS, on which the carriage l4 and the photocells l2 and I3are mounted, are parallel to the face 3 and the defining dimensions ofthe apparatus are: prism angle=60, angle of incidence of light into face3:45, distance of the point at which light enters face 3 from the apexof prism-: inches; then the distance between face 3 and the plane of thephotocells which will give a lateral displacement of the beam equal to0.10 inch when a change of 1 per cent in sugar concentration has takenplace, is 28 inches, the beam intersecting the plane of the photocellsabout 9 inches from that point in the latter plane perpendicularlyopposite the point where the light enters face 3.

Changes in the sugar concentration will result in displacements of thebeam equal to 0.10 inch for each 1 per cent change in concentration, thetemperature being maintained at 68 F. The sensitivity of the instrumentcan be doubled to measure or control the concentration to the nearest0.5 per cent, either by doubling the distance between the plane of thephotocells and the face 3 or by halving the width of the beam to 0.05inch, an desired degree of sensitivity being achieved by either or bothof these means.

It is thus seen how the apparatus shown in Fig. 1 may be used to measureand record changes in the concentration of a sugar solution and how theexact position of the various elements may be calculated in advance. Itis also evident that such calculations are possible without advanceknowledge of the exact emission characteristics of the light source andphotocells, the transmission of the solution or the electrical constantsof the amplifying devices. Calibration of the systern in terms of theseelements is unnecessary since it is required only to adjust photocellsensitivity so that the magnitude of changes in light flux of the orderto be exposed will activate the amplifiers. By computations similar tothose in the preceding paragraph one may calculate where to place thestops 28 and 29 of Fig. 2 or the mirrors 4| and 42 of Fig. 3 so that bypassing a beam of sodium D light through the sugar solution in acontinuous concentrator (or in a sampling tube connected with aconcentrator), one may automatically increase the rate of feeding steamto a concentrator if the concentrating of the sugar solution lags or,conversely, bleed air into the vacuum line of the concentrator if theconcentration exceeds a. desired maximum.

Another example of the use of my invention is in the extraction ofpyridine cases with dilute sulfuric acid from the heavy oil residue ofcoaltar distillations. The difference in refractive indices of pyridineand 5 per cent sulfuric acid solution would be such that measurement orcontrol of the solution to within the nearest 1 per cent of pyridinecould be obtained by measuring or controlling the refractive index toapproximately .0011 to .0012. Since, as has been pointed out in thedescription of the instrument, it is possible to expand the opticaldimensions of the instrument so that any desired degree of sensitivitycan be obtained, the principal limitation to the sensitivity which canbe achieved will be for practical purposes the closeness of control overtemperature. If this can be controlled or compeniated for to the nearest1 (3., corresponding to a change in refractive index of less than 0.0001in the case of dilute aqueous solutions, it is evident that theconcentration of the acid aqueous phase containing pyridine bases couldbe controlled or measured to within 0.1 per cent pyridine.

The apparatus of Fig. 1 may be used to record the pyridine content ofsuch an extract at all times. Apparatus such as shown in Figs. 2 and 3may be used to control the operation as desired. Turbidity in theextract will not interfere with the accurate functioning of theapparatus.

Similarly, phenols and cresols are customarily removed from the portionof coal-tar distillates boiling between 200 and 270 C. by agitating thelatter with 10 to 15 per cent caustic solution. forming sodium phenolateand sodium cresylates in the aqueous phase. The difference in therefractive indices of the salts thus formed and the raw caustic solutionis of a magnitude such that a change in refractive index of 0.0020corresponds to a change of 1 per cent in the concentration of the salt.Thus, if the solution temperature be controlled or compensated for towithin 1 C., the concentration of the solution can be measured orcontrolled to within 0.05 per cent of the extracted salt.

The following example illustrates a. use for the apparatus shown in Fig.4 in which changes in the refractive dispersion of two beam elements areutilized. In the operation of liquid-liquid extraction columns, theratio and volume of the heavy and light feeds at any particular instantare usually functions of the efliciency of separation being effected, asjudged by the compositions of the extract and raflinate effluents. In acase where ethyl alcohol is being removed from a benzene-alcohol mixtureb extraction with water, for example, it may be desirable to obtain apractically benzene-free extract and. therefore, to control theoperation of the column by the benzene content of the extract.

For this example the following terminology will be used:

nc=refractive index at 6563 A.

no=refractive index at 5893 A.

nc' refractive index at 4341 A.

d=dispersion, TLG'7ZC Ann and Ad=changes in refractive index anddispersion, respectively The following physical properties are from theInternational Critical Tables, volume VII:

t C. no 0' i 1.33300 1.33115 1.34035 920 1.30342 1.36062 1.37011 949Benzene 20 1. 50144 1.40663 1. 52361 2, 608

moment to moment depending on the volume ratio of light to heavy feed.the composition of the benzene-alcohol mixture, etc. On the other hand,the contribution of small amounts of benmight then be expressed by thevalue zene to the dispersion of the extract would be 5 large relative tothe nearly equal dispersions of =25 alcohol and water and would,therefore, provide 31-68-311) zgglfrffilctive means of controllingoperation of the l ig sg g f! clgmparmg the Ad va ues co osl This couldbest be illustrated by calculating the 10 Simngfly, a fi gtggfcomposmons C and no, Ann, :1 and Ad for each of the compositions D v 1th t t th t 1 represented by the following conditions of operre 8? s a agrea at an twen y o d in anew crease in benzene content, with acorresponding I increase 1n Ad, would be necessary to produce the A.Extract containing 31 per cent alcohol and no Same n as occasioned yincreasing the 81601101 benzene content to 48.3 per cent (compositionB). B. Alcohol content increased to give a Ad 10 of A further andimportant use of dispersion 88 5.0--no benzene a means of measuring orcontrolling composi- C. Thirty-one percent alcohol plus an m nt f tionsis found in the many instances-including benzene to give the same Ad 10as comc es involving binary mixtures-Where t s position B (=50)difficult, undesirable or impracticable to main- D. Thirty-one percentalc hol plus an a t tain the temperature of the measured fluid conofbenzene to give the same Ann as composistant or to measure or compensatefor temperation B ture changes. This includes, for example, cases E.Alcohol content increased to give the same W r p ra ur ch n e re rapi ndl r Ann as composition C n benzene Under such conditions it may often bedesirable The properties of these compositions are sumi dispersion. i ameans of measuqing or marized in the following table: rollingcomposition, inasmuch as dlSpGISlOIhlS virtually unaffected bytemperature, and the dis- Per persion of a substance is, in general,substan- Per cent Ai'lnXlO Adxlm tially independent'of its temperaturebut prosat? 11K, Benportional to its refractive index at any wave zenelength in the region in which the dispersion is measured. 2% g 8 313% g"5], 5 The following data, computed from informa- 135344 44 tion givenin the International Critical Tables I $123 8' {3%. 22 05% f (volumeVII) shows that the dispersion of a substance is considerably lessaffected by tem- International Critical Tables, volume v11. peraturechanges than is its refractive index at At this composition mixtureseparates into two phones. 40 a particular wave length:

Substance Water 1 2?? fi g 525K111 Benzol Temp. range, 0. 10-10 2a4-30m22445.0 10. e415 10-30 AnD(=1h 1ll .00800 0.0054 0.02100 0. 010110.00005 Ann per o. 10= 15 22 51 44 00 Wave length range A. 6563-58935803-4341 6563-6893 6563-5893 6563-5893 Ad =d.,-d 0.00000 0.000000.00044 0.0000s 0.00004 Ad per 0. (x10 0.10 0.30 0.83 0. 22 0. 21

Examination of the values in the above table shows that dispersion wouldbe a much more eflective means of detecting small amounts of benzenethan would the refractive index at a particular wave length. If, forexample, the relative sensitivity to changes in benzene content asmeasured by dispersion be compared to that measured by refractive indexat a single wave length on this basis: that, in the one case(composition B) the alcohol content would have to increase from 31 to48.3 per cent to give a Ad equal to that resulting from an increase inbenzene from zero to 0.28 per cent (composition C), whereas in anothercase (composition E), the Ann caused by this small amount of benzenewould correspond to an increase in alcohol from 31.0 to only 31.68 percent; the ratio We observe from the above calculations that the changein refractive index per degree for the temperature range noted ascompared with the change in dispersion for the wave lengths noted is forwater as 15 is to 0.15; for sulfuric acid as 22 is to 0.30; forZ-furaldehyde as 51 is to 0.83; for ethyl alcohol as 44 is to 0.22; andfor benzol as is to 0.27. It is, therefore, clearly patent that, atleast at times, temperature changes may be dis regarded for measurementsor controls made on the basis of dispersion, whereas on the basis ofrefractive index no considerable temperature change without correctioncan be tolerated. In such cases the apparatus of Fig. 4 can be used togreat advantage.

Bearing in mind that the illustrations and examples are cited merely toindicate possible adapll tations of the invention, it is apparent thatthe invention will find many commercial applications. It is not limitedto use with liquids, but may be used also with gases, as, for example,for controlling the admixture of air and butane, etc.

What I claim is:

1. The process of utilizing changes in the refractive index of a fluidfor control purposes which comprises collimating beam of monochromaticlight, passing the collimated beam through the fluid and causing theemergent beam to fall in the space between two surfaces adapted forutilization of the light energy impinging thereon. which space in thedirection of lateral travel of the beam is not substantially wider thanthe width of the beam, and as a change in the refractive index of thefluid causes the beam to move from the space to one of the surfaces,causing both surfaces to move in the direction the beam has moved sothat the beam again falls in the space between them.

2. The process of utilizing changes in the refractive index of a fluidfor control purposes which comprises passing a beam of collimatedmonochromatic light through the fluid and causing the emergent beam tofall in the space between two surfaces adapted for utilization of thelight energy impinging thereon, which space in the direction of lateraltravel of the beam is not substantially wider than the width of thebeam. and as a change in the refractive index causes the beam to movefrom the space to one of the surfaces, causing the cells to move so thatthe beam again falls in the space between them, and as the cells move,bringing about a change in the fluid to restore its original refractiveindex, and as this is restored, returning the cells to their originalposition.

3. The process of utilizing for control purposes changes in thedispersion of two beam elements of collimated radiant energy ofsegregated wave lengths passed through a prism containing a fluid whichcomprises passing one of the beam elements between two surfaces adaptedfor utilization of the light energy impinging thereon and as a resultthereof causing said surfaces to follow said beam element as therefractive index of the fluid in the prisim changes so that the beam isalways between said surfaces, the other element being thereby caused tochange its position with respect to a photosensitive surface which ismaintained in a flxed relation with the aforesaid two surfaces.

4. The process of utilizing changes in the refractive index of a fluidfor control purposes which comprises passing a beam of collimatedmonochromatic light through the fluid and caus ing the emergent beam tofall in the space between two surfaces adapted for utilization of thelight energy impinging thereon, which space is wider than the beam bythe amount of lateral travel which the beam will make as it fluctuateswithin the allowable limits of concentration of the fluid. and as theconcentration fluctuates beyond said limits, causing the beam to fall onone of said surfaces and thereby set in motion forces which return theconcentration of the fluid to within said limits.

5. The process of utilizing changes in the refractive dispersion of afluid for control purposes which comprises passing through the fl'uid abeam of collimated light whose radiant energy has been reduced to twosegregated monochromatic wave lengths and causing one of the wavelengthelements of the beam to fall in the space between two surfaces adaptedfor utilization of the light energy impinging thereon, which space inthe direction of lateral travel of the beam is not substantially widerthan the width of the beam; and as a change in the refractive indexcauses the beam to move from the space to one of the surfaces, therebycausing both surfaces to move in the direction the beam has moved sothat the beam again falls in the space between them; and as changes inrefractive dispersion result in changes in the angular separationbetween the wave-length elements of the beam, causing the other waveelement to change its point of im pingence with respect to otherphotosensitive surfaces associated only with this wave-length element,and thereby as the angular separation changes, bringing about a changein the fluid to restore its original refractive dispersion.

6. The process of utilizing for control purposes changes in thedispersion of two beam elements of collimated radiant energy ofsegregated wave lengths passed through a prism containing a fluid whichcomprises passing one of the beam elements between two surfaces adaptedfor utilization of the light energy impinging thereon, and moving saidsurfaces to follow said beam element as the refractive index of thefluid in the prism changes so that the beam is always between saidsurfaces, the other element being caused to initiate responses in eachof a plurality of other light-sensltive surfaces as the refractivedispersion and thus the relative position of the two beams vary.

7. Apparatus for the utilization of changes in the refractive index of afluid which comprises a hollow prism adapted to contain the fluid, theprism having faces transparent to radiant energy, two. surfaces adaptedfor utilization of the light energy impinging thereon, each connected toamplifying means and other means adapted to move both surfaces in thedirection of either surface as light falls thereon, and a source of abeam of monochromatic light and means for collimating the light, thepieces of equipment being arranged so that a beam from said sourcefalling on the prism is refracted so as to fall approximately in thespace between the surfaces.

8. Apparatus for the utilization of changes in the refractive index of afluid composed of a hollow prism adapted to contain the fluid, the prismhaving faces transparent to radiant energy, two surfacesadapted forutilizationv of t. e light energy impinging thereon, each connected toamplifying means, a source of a beam of collimated monochromatic light,the space between the surfaces being wider than the beam by the amountof lateral travel which the beam will make as the concentration of thefluid fluctuates within allowable limits, and means actuated by lightfalling on either of said surfaces for returning the concentration ofthe fluid to within said allowable limits.

9. Apparatus for utilization of changes in the refractive dispersion ofa fluid which comprises a hollow prism to contain the fluid, the prismhaving faces transparent to radiant energy, a source of a beam ofcollimated light whose radiant energy is reduced to two monochromaticwave lengths segregated in the energy spectrum, the beam being directedonto the prism and refracted into two elements of different wavelengths, on opposite sides of one of said refracted elements surfacesadapted for utilization of the light energy impinging thereon with meansactuated thereby for causing said surfaces to follow said element sothat said surfaces are at all times on opposite sides of said element,and at least one other surface adapted for utilization of the lightenergy impinging thereon which other surface is maintained in a fixedrelation to said first-mentioned surfaces and is in the range of thepath of the other beam element.

10. Apparatus for utilization of changes in the refractive dispersion ofa fluid which comprises a hollow prism to contain the fluid, the prismhaving faces transparent to radiant energy, a source of a beam ofcollimated light whose radiant energy is reduced to two monochromaticwave lengths segregated in the energy spectrum, the beam being directedonto the prism and refracted into two elements of different wavelengths, on opposite sides of one of said refracted elements surfacesadapted for utilization of the light energy impinging thereon with meansfor utilizing the same to cause said surfaces to follow the element sothat said surfaces are at all times on opposite sides of the element,and a plurality of photosensitive surfaces adapted to be intercepted bytheother beam element as changes in the fluid cause chan es in therefractive dispersion thereof.

11. The process of utilizing changes in the refractive index of a fluidfor control purposes which comprises passing a beam of collimatedmonochromatic light through the fluid and causing the emergent beam tofall in the space between two surfaces adapted for utilization of thelight energy impinging thereon, which space is wider than the beam bythe amount of lateral travel which the beam will make as it fluctuateswithin the allowable limits of concentration of the fluid, and as theconcentration fluctuates beyond said limits, causing the beam to fall onone of said surfaces and thereby set in motion a desired force.

12. The process of utilizing changes in the refractive dispersion of afluid for control purposes which comprises passing through the fluid abeam of collimated light whose radiant energy has been reduced to twosegregated monochromatic wave lengths and causing one of the wave-lengthelements of the beam to fall in the space between two surfaces adaptedfor utilization of the light energy impinging thereon, which space inthe direction of lateral travel of the beam is not substantially widerthan the width of the beam; and as a change in the refractive indexcauses the beam to move from the space to one of the surfaces, causingboth surfaces to move in the direction the beam has moved so that thebeam again falls in the space between them, and as changes in refractivedlspersion result in changes in the angular separation between thewave-length elements of the beam, causing the other wave element tochange its point of impingence with respect to other photosensitivesurfaces associated only with this wave-length element, and as theangular separation changes, setting a desired force in motion.

13. Apparatus for the utilization of changes in the refractive index ofa fluid composed of a hollow prism adapted to contain the fluid, theprism having faces transparent to radiant energy, two surfaces adaptedfor utilization of the light energy impinging thereon, each connected toamplifying means, a source of a beam of collimated monochromatic light,the space between the surfaces being wider than the beam by the amountof lateral travel which the beam will make as the concentration of thefluid fluctuates within allowable limits, the amplifying means beingconnected with control means.

14. The process of utilizing changes in the refractive index of a fluidfor control pu poses, which comprises collimating a beam of lightcontaining at least one monochromatic element to produce a beam in whichthe light rays are at least substantially collimated, passing thecollimated light through the fluid and intercepting the refractedmonochromatic element by a surface adapted to the utilization of thelight energy impinging thereon as changes in the refractive index of thefluid cause changes in the direction of the beam element, and movingsaid surface as the direction of the beam changes so as to maintain thesurface in a substantially constant relation to the beam regardless ofthe direction of the beam.

15. Apparatus for the utilization, for control purposes, of changes inthe refractive index of a fluid, which includes a prism with faces transparout to radiant energy and adapted to conaain the fluid, a sourceof a beam of monochromatic light which impinges on the prism, meanslocated between said source and said prism for substantially collimatingthe light beam, two photosensitive surfaces connected individually withmeans for utilization of light energy impinging thereon, and meansoperated by said light-utilizing means for maintaining said surfaces insubstantially the same relative position to the beam as changes in therefractive index of the fluid cause changes in the refractive index ofthe beam.

16. Apparatus for the utilization of changes in the refractive index ofa fluid which comprises a hollow prism adapted to contain the fluid, theprism having faces transparent to radiant energy, a source of a beam ofmonochromatic light and means for collimating the light, and twophotosensitive surfaces spaced about the width of the beam andpositioned so that the beam after being refracted by the fluid fallsbetween them, said surfaces being connected individually throughamplifying means to means responsive thereto for moving both surfaces inthe direction of either surface as light falls thereon so as to keep thesurfaces on opposite sides of the light beam.

17. Apparatus for the utilization of changes in the refractive index ofa fluid, comprising a hollow prism adapted to contain the fluid, theprism having faces transparent to radiant energy, a source of a beam ofcollimated monochromatic light, two photosensitive surfaces spaced aboutthe width of the beam and positioned so that the beam after beingrefracted by the fluid falls between them, means responsive to lightfalling on either of said surfaces for moving said surfaces in thedirection of the surface affected by the light,

and recording means for moving therewith.

18. Apparatus for the utilization of changes in the refractive index ofa fluid, comprising a hollow prism adapted to contain the fluid, theprism having faces transparent to radiant energy. a source of a beam ofcollimated monochromatic light, two photosensitive surfaces spaced aboutthe width of the beam and positioned so that the beam after beingrefracted by the fluid falls between them, means responsive to lightfalling on either of said surfaces for moving said surfaces in thedirection of the surface affected by the light, recording means, and inthe path of said movement of the surfaces and all means movingtherewith, means for initiating action on equipment which restores thefluid to its original concentration.

ROBERT M. PIERSON.

(References on following page) REFERENCES crmn Numm 1,806,198 Hardy May19, 1931 The following references are 0! record in the 1,939,088 BtyerDec. 12, 1933 file of this patent: 1,955,315 Styer Apr. 1'7, 1934 UNITEDSTATES PATENTS 5 2,042,281 l y 1938 N be 2,091,303 Brelstord Am. 31,1937 um I Name Date 2,113,436 Williams Apr. 5, 1938 1,471,342 Logan 21923 2,335,1 3 s it 33, 1943 1,774,961 Buchholz Sept. 2, 1930Certificate of Correction Patent No. 2,483,102 September 27, 1949 ROBERTM. PIERSON It is hereby certified that error appears in the printedspecification of the above numbered patent requiring correction asfollows:

Column 7, line 45, for the word exposed read expected;

and that the said Letters Patent should be read with this correctiontherein that the same may conform to the record of the casein the PatentOfiice.

Signed and sealed this 24th day of January, A. D. 1950.

THOMAS F. MURPHY,

Am'atant Ooma'uionor of PM.

